Process of electrolytically improving the clarity of sulfonic acids



United States Patent Office Patented August 30, 1966 3,269,927 PROCESS OF ELECTROLYTICALLY IMPROVING THE CLARITY F SULFONIC ACIDS Howard W. Bost, Bartlesville, Okla., assignor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Filed Oct. 1, 1962, Ser. No. 227,533 5 Claims. (Cl. 204-131) This invention relates broadly to the treatment of sulfonlc acids. In one particular aspect this invention relates to an improved method of improving .the color of sulfonic acids such as alkanesulfonic acids.

The sulfonation reaction has been applied to numerous types of organic materials. For example, a wide variety I of alkanesulfonic acids are produced commercially for such uses as detergents, emulsifiers and intermediates for the synthesis of other chemicals. While a number of methods are known and used for the production of these alkanesulfonic acids, a large percentage of these acids are formed by the oxidation of mercaptans', sulfides, disulfides and the like. One problem which is frequently encountered in the production of sulfonic acids, especially alkanesulfonic acids, is the dark color of the product materials formed. While the color of the product generally does not interfere with chemical reactions involving these products, customer acceptance of highly colored materials is poor and therefore, customers may refuse to utilize these products for other purposes.

Although several expedients have been proposed or used for decoloriing sulfonic acids, it can be safely stated that there is still considerable room for improvement, particularly with regard to the provision of a practical process for minimizing and reducing color in sulfonic acids. The present invention relates to an improved process for decolorizing sulfonic acids whereby a sulfonic acid is treated without the addition of diluting materials to effect decolorization.

Accordingly, an object of this invention is to provide a method for decolorizing sulfonic acids.

Another object of this invention is to provide a process for effecting decolorization of sulfonic acids without the addition of extraneous materials which may dilute or otherwise decrease the purity of the purified sulfonic acid.

Other aspects, objects, as well as the several advantages of the invention are apparent from a study of this disclosure and the appended claims.

It has been found that color bodies and color-forming matcrals present in sulfonic acids can be effectively removed from the acid by subjecting the color-contaminated sulfonic acid to a direct current electrical field.

Therefore, according to the invention, there is provided a process for the decolorization of sulfonic acids, especially alkanesulfonic acids which comprises subjecting a colorcontaminated sulfonic acid to a relatively high voltage and a relatively high current density direct current electrical field.

The sulfonic acids that can be treated according to the process of the invention are those which contain color bodies or color forming materials which can be effectively removed or broken down by subjecting the acid to a direct current electrical field as defined herein. More particularly, and preferably, the invention is applied to the treatment of alkanesulfonic acids which generally contain from 1 to 20, inclusive, carbon atoms, although higher molecular weight sulfonic acid materials can be treated. It is within the scope of the invention to treat sulfonic acid mixtures as well as refined sulfonic acids. However, it is preferred to treat sulfonic acid reaction mixtures having poor color properties and which are particularly subject to subsequent color formation during storage or handling.

Many of the sulfonic acids that can be treated according to the invention are liquids and can be treated as such,

but many of the sulfonic acids are solids and it is preferred to form solutions of these with an inert diluent solvent prior to subjecting same to the direct current electrical field. Suitable inert diluents that can be employed include the low boiling hydrocarbons such as propane, butane, pentane, hexanes, octanes and the like. Otherhydrocarbons that can be employed include the cycloparafiins, such as cyclohexane, methylcyclohexane and the like. Aromatic hydrocarbons such as benzene, toluene and the like, can also be used. It is also within the scope of the invention to employ aqueous solutions of sulfonic acids for treatment with the defined direct current electrical field.

The electrical field intensity utilized in the practice of this invention will vary somewhat depending upon the particular sulfonic acid being treated, but in general the voltage will range from 1 to 10 volts. The current density of each electrode will generally range from 10 to 200 amps per square decimeter, preferably from to amps on the same basis. When subjecting the sulfonic acids to direct current according to the invention, it is preferred to employ shiny platinum electrodes. As will be evident to those skilled in the art, with the larger electrodes, higher total amperages will be used. The voltage range defined is a relatively high voltage in electrolytic processes, and this is required in view of the relatively poor conductivity of sulfonic acids. In the case ofhigher molecular weight alkanesulfonic acids wherein an inert reaction diluent is employed, it is within the scope of the invention to add electrical conducting materials to the acid solution to increase its conductivity.

The process of the invention is carried out at relatively low temperatures, ordinarily ranging from 10 to 50 C., and more often about 25 C. The time required for electrolysis will depend upon the voltage applied, the current density, the color of the sulfonic acid prior to passing the current through the material, and the desired final color of the material being treated. However, generally speaking, treatment times ranging up to about 30 minutes are satisfactory for effecting substantially complete decolorization of alkanesulfonic acids.

In carrying out the process of the invention, a sulfonic acid or mixture thereof can be subjected to the direct current electrical field as defiend above, either in a continuous, semi-continuous or batch manner depending upon the available equipment. Suitable apparatus for carrying out electrolytic treatment are known in the art and need not be described in detail herein. In a continuous operation, a solution containing at least one alkanesulfonic acid is passed between electrodes exerting a field intensity as defined above for a period of time sufficient to effect the desired degree of decolorization. In a batch operation, suitable electrodes can be immersed in a solution of a sulfonic acid and the solution can be subjected to a direct current electrical field, as defined, until the solution becomes clear.

A beter understanding of the invention and the effectiveness of the invention for decolorizlng alkanesulfonic acids will be obtained upon reference to the following specific example which is not intended, however, to be unduly limitative of the invention.

Example A sample of commercial methanesulfonic acid (Pennsalt) of dark color was treated in the following manner. A 35 gram sample of this liquid was placed in an open beaker and 2 shiny platinum electrodes were immersed in the acid. A direct current electrical field was then applied across the electrodes, using 5 volts at 6.5 amps for 5 minutes. The surface area of each of the platinum electrodes was approximately 1 sq. in., therefore, the surface area of each electrode in square decimetcrs was 0.0645.

3 The calculated current density of each electrode was 6.5/0.0645 or 100.8 amps/sq. decimeter. The original color of the methunesulfonic acid was 1-1 on a Helige color scale. After treatment with the direct current as described above, the material had a Helige color of 1 (essentially water white).

As will be evident to those skilled in the art many varialiens and modifications of this invention can be practiced in view of the foregoing disclosure. Such variations and modifications are clearly believed to come within the spirit and scope of the invention.

I claim:

1. A process for improving the color of alkanesulfonic acids having from 1 to 20, inclusive, carbon atoms per molecule which comprises subjecting same in an electrolytic cell to a direct current electrical field having a current density of each electrode ranging from -120 amps. per square decimeter for a period of time suflicient to substantially decolorize said acid.

2. A process for improving the color of alkanesulfonic acid which comprises passing a direct current electrical field through an alkanesulfonic acid having from 1 to 20, inclusive, carbon atoms in an electrolytic cell at a temperature ranging from 1050 C. for a period of time ranging up to about 30 minutes sufficient to substantially 'decolorize said acid, said direct current having a current density of each electrode ranging from 80-120 amps. per square decimeter, and recoving said acid substantially free of said color.

3. In a process for the formation of an alkanesulfonic acid formed by reacting a hydrocarbon with a sulfonating agent and wherein said acid reaction product contains color bodies and color formers, the improvement which comprises subjecting said acid in an electrolytic cell to a direct current electrical field having a current density of each electrode ranging from about 10-120 amps. per square decimeter for a period of time up to about 30 minutes sufiicient to elfect decolorization of said acid, and recovering said acid substantially free of color.

4. A process for decolorizing methanesulfonic acid which comprises subjecting same in an electrolytic cell to a direct current electrical field having a current density of each electrode of about amps. per square decimeter for a period of time of about 5 minutes at room temperature to decolorize said methanesulfonie acid.

5. A process according to claim 1 wherein the electrodes used during the electrolysis reaction were constructed of platinum.

References Cited by the Examiner UNITED STATES PATENTS 1,698,450 1/ 1929 Pungs et al. 204-431 2,525,942 10/1950 Proell 204-46 2,808,372 10/ 1957 Conwell et al 204l3'1 2,823,178 2/1958' Ritter 204l31 2,824,831 2/ 1958 Conwell et a1. 204-431 JOHN H. MACK, Primary Examiner.

MURRAY TILLMAN, Examiner. L. G. WISE, H. M. FLOURNOY, Assistant Examiners. 

